1. Field of the Invention
The present invention relates to an interlock system and an image forming apparatus, such as a copier, a printer, a facsimile machine, etc., incorporating the interlock system, and in particular to an interlock system operated in conjunction with opening and closing of a cover provided to an image forming apparatus, and an image forming apparatus incorporating the interlock system.
2. Description of the Background Art
In general, an image forming apparatus includes a component, such as a processing unit, etc., within an apparatus body. Accordingly, when the component is to be replaced, the interior of the image forming apparatus body must necessarily be accessible. Further, when sheet jam occurs in the apparatus body, a user also needs to access the interior of the image forming apparatus to remove the sheet causing the jam.
For that purpose, the image forming apparatus generally includes an openably closable member, such as an exterior cover, a lid, etc., openable with regard to the apparatus body to allow a user to access thereto to replace the component, or remove the jammed sheet.
One complication is that, such an image forming apparatus generally includes an electronic instrument as a load that needs a high voltage, thereby generating heat of high temperature, and which is, exposed when the cover is opened.
To ensure safety of a user even when the cover is opened, the image forming apparatus sometimes includes an interlock system having an interlock switch or the like operating in conjunction with a of the cover. For example, a connection between a power supply and the electronic instrument it supplied with power is cut by the interlock system on an electric circuit when the cover is opened.
Various interlock systems have been proposed as illustrated in FIGS. 21A and 21B.
For example, as shown in FIGS. 21 and 22, a conventional interlock system 110 is included in an image forming apparatus body 100 to detect opening and closing of an upper cover 101 and an exterior cover 102 with an interlock switch 111. Plural strikers 101a and 102a are provided on the upper cover 101 and the exterior cover 102 to operate the interlock system 110.
Specifically, when the external cover 102 is closed in the interlock system 110, an arm 113 is pressed by the striker 102a and moves to the left in the drawing. Further, when the upper cover 101 is closed in addition to the external cover 102, an actuation lever 114 is pressed by a striker 101a and moves downward in the drawing. Consequently, a swingable lever 111a of the interlock switch 111 is pressed and is turned on by the actuation lever 104. Further, a contact surface of the striker 101a contacting the actuation lever 114 is inclined at a prescribed angle (theta) θ, so that the actuation lever 114 can swing counterclockwise in the drawing.
In this way, the opening and closing of both the upper cover 101 and the exterior cover 102 are detected by decreasing the number of separately and independently necessitated interlock switches from two to one.
In such an interlock system, when one of the fixing unit cover and the original document reader cover is opened, the striker lever and the pushing lever operate in conjunction with opening of the two covers and turn on the interlock switch, so that an interlock signal is outputted therefrom in response thereto.
However, when the external cover 102 is opened while the upper cover 101 is closed in the conventional interlock system 110, the actuation lever 114 swings upward being affected by a return reactive force Fa of the swingable lever 111a of the interlock switch 111, while the arm 113 moves to the right therein as shown in FIG. 22.
Consequently, pressure applied to the swingable lever 111a swings counter clockwise and the interlock switch 111 of the interlock system 110 is turned off.
During the movement of the arm 113 and the actuation lever 114 on an inclination surface of the striker 101a, a sliding resistance is created due to an inclination angle θ (theta) of a contact surface between the striker 101a and the actuation lever 114 and a friction coefficient μ thereof.
Consequently, the arm 113 cannot be moved a prescribed length simply by the return reactive force Fa of the swingable lever 111a due to the above-mentioned sliding resistance. As a result, the arm 113 likely cannot reach a position where the interlock switch 111 is completely turned off.
To make sure that the arm 113 can reach such a position, a bias spring 113a may be provided to bias the arm 113 to the right in FIG. 22 by a biasing force Fb.
Thus, when a bias force Fb of the bias spring 113a is increased, movement of the arm 113 is ensured. However, when the bias force Fb is excessively increased, it serves as a resistance against a closing of the external cover 102 and increases the force required to close the cover. Further, since a stress caused by the bias spring 113a remains even when the external cover 102 is closed, an internal stress (i.e., a residual stress) in a member that engages the bias spring 113a increases, so that the member likely deforms due to creep phenomenon.
Accordingly, the bias force Fb needs to be appropriately determined within a narrow prescribed range to ensure appropriate movement of the arm 113 while suppressing an excessive bias force Fb in the conventional interlock system 110.
For that reason, shortage of a return reactive force Fa of the swingable lever 111a needs to be compensated considering the inclination angle θ (theta) of the contact surface between the striker 101a and the actuation lever 114 and the friction coefficient μ thereof, resulting in increasing cost due to increasing complexity and the need for finer parts tolerance.